Golf balls which have been known to the art generally include one-piece golf balls, two-piece golfs ball and multi-piece golf balls (e.g. three-piece golf balls, four-piece golf balls, etc.). Intensive study has been made for enhancing the flight performance of the golf ball and increasing flight distance.
The multi-piece golf ball can be one having an intermediate layer between a core and a cover, which has been proposed in Japanese Patent Kokoku Publication Nos. 63 (1988)-61029 and 3 (1991)-3501 and Japanese Patent Kokai Publication No. 2 (1990)-228978. In the proposed three piece solid golf balls, the specific gravity of the intermediate layer is made higher then that of the core so as to increase the moment of inertia of the golf ball. In other words, when the golf ball is hit by a golf club, spin is put on the golf ball and a dynamic lift is exerted in the line normal to the flight curve of the golf ball. However, since a force negative to the ball running direction is exerted on the ascending of the golf ball immediately after launching in the horizontal direction partial force of the dynamic lift, large ball speed immediately after launching is reduced by the dynamic lift. To the contrary, since the dynamic lift due in spin is exerted to the running direction as a positive force in the horizontal direction partial force on descending after the golf ball has already passed the peak position, the dynamic lift on the descending of the golf ball is preferably large so as to increase the flight distance. Accordingly, in order to increase the flight distance of the golf ball, the spin amount on ascending of the golf ball immediately after launching is preferably small and the spin amount on descending of the golf ball is preferably large. In order to increase the flight distance, the larger the moment of inertia of the golf ball, the better. However, when the core of golf balls is formed from a rubber composition, there is a limitation for increasing the moment of inertia, because the rubber itself has a relatively heavy weight.
Japanese Patent Kokai Publication No. 6 (1994)-170012 suggests to lighten the core, wherein the core is composed of a molded article of vulcanized rubber containing a light-weight filler, a resin molded article containing a light-weight filler, or a molded foamed article of rubber or resin. However, this suggestion has a drawback that, since a large amount of the filler is contained in the intermediate layer, the rebound characteristics of the golf ball is low and the flight distance is reduced.